If the whole gill extends down the stem, it is called decurrent. The edge of a decurrentgill is usually not horizontal, but approaches the stem at a slant, so the gill constantly gets wider as it approaches the stem.
This type of gill attachment is #3 in the numbered diagram.

This attachment is #4 in the diagram. It is the last type of attachment on which there is general agreement. The rest of them are the way I use the terms in this website, and are quite reasonable, but it will be easy for you to find people who disagree with me. For a discussion of why this is so, see the entry for natural language.

Sinuate is also sometimes used to describe a long edge, like the edge of a gill or the cap, which is smoothly wavy, like a series of swells in the ocean. The margin of the cap of this Phellodon tomentosus is sinuate.

Drawing #8 in the numbered diagram illustrates an attachment that is fairly common, seems to me to be quite distinct from any of the others, and has no specific name.
It seems to me that some people call this adnexed, and others call it emarginate.

Another phenomenon to take into account is that as the mushroom dries out and the cap lifts, gills that were attached to the stem sometimes secede: they pull away from it. The gills on the upper right of this picture are subdecurrent, as they ought to be. The gills on the lower right snapped away from the stalk, with an audible pop, as I was turning the mushroom over to take this picture.